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System Design Interview Kit

Practise system design step by step: estimation, resilience patterns, then 15 reference designs from URL shortener and rate limiter to message queue, booking and LLM serving.

Step 1

Learning

  1. Back-of-Envelope Estimation and Capacity Model Template

    Full

    Reference latency and unit tables, assumptions register, QPS, storage, bandwidth, cache, server and cost formulas, worked example, sensitivity, traceability

    Jeff Dean latency numbers (LADIS 2009)

  2. Resilience and Load Shedding Design Template (Retries, Circuit Breakers)

    Full

    Failure model, deadlines, retries with jitter and budgets, circuit breakers, bulkheads, backpressure, criticality-based shedding, degradation, fault tests

    Google SRE book ch. 21-22; Amazon Builders' Library

  3. System Design Document Template

    Full

    System design at scale – requirements, capacity estimates (KaTeX), API, data model, HLD, deep dives, reliability, cost, trade-offs

Step 2

Reference designs

  1. URL Shortener System Design Template (Reference Design)

    Full

    Capacity (KaTeX), API, base62 key generation and collisions, 301 vs 302, caching, click analytics, abuse protection, custom aliases, expiry, multi-region

    RFC 9110 (redirect status codes)

  2. Rate Limiter System Design Template (Reference Design)

    Full

    Distributed rate limiter: token bucket vs window algorithms, atomic Redis scripts, multi-region shares, 429 headers, fail-open

  3. Distributed Key-Value Store System Design Template (Dynamo-Style)

    Full

    Consistent hashing, vnodes, quorums (R+W>N), vector clocks vs LWW, hinted handoff, Merkle anti-entropy, gossip, LSM compaction, cache eviction, hot keys

    Dynamo (DeCandia et al., SOSP 2007)

  4. Distributed Message Queue System Design Template (Kafka-Style Log)

    Full

    Partitions, log segments, retention, acks and idempotence, consumer groups, offsets, delivery semantics, ordering, ISR replication, backpressure, DLQ, schemas

    Apache Kafka 4.3 documentation; Kafka paper (NetDB 2011)

  5. News Feed System Design Template (Reference Design)

    Full

    Social feed: hybrid fan-out on write and read, celebrity threshold, ranking pipeline, feed cache, snapshot pagination, media

  6. Chat System Design Template (Reference Design)

    Full

    Real-time 1:1 and group chat: WebSocket gateways, per-conversation ordering, fan-out, receipts, offline sync, push, E2EE

  7. Notification Service System Design Template (Reference Design)

    Full

    Push, email, SMS and in-app: templates, preferences and opt-out, priority queues, caps, provider failover, retries, dedup

  8. Ticket and Hotel Booking System Design Template (Reference Design)

    Full

    Seat and room inventory, holds with TTL, overbooking math, conditional writes, idempotency, payment saga, waiting room, search vs booking paths

  9. Search Autocomplete System Design Template (Reference Design)

    Full

    Typeahead: trie/FST/edge n-gram index, popularity and recency ranking, query-log pipeline, edge cache, latency budget, safety

  10. Job Scheduler System Design Template (Reference Design)

    Full

    Distributed scheduler: cron, delayed and one-off jobs, leases and visibility timeouts, fencing, idempotent handlers, retries, DLQ

  11. Payment Ledger System Design Template (Reference Design)

    Full

    Payments and double-entry ledger: idempotency keys, payment state machine, PSPs, outbox, reconciliation, audit, PCI DSS scope

  12. Ride-Hailing Dispatch System Design Template (Reference Design)

    Full

    Ride matching: location ingestion, H3/geohash index, batched matching, ETA, trip state machine, single assignment, surge note

  13. Video Streaming System Design Template (Reference Design)

    Full

    Video upload and ABR streaming: chunked transcoding, renditions ladder, CMAF HLS/DASH, CDN, DRM note, view counts, storage tiers

  14. Collaborative Editing System Design Template (Reference Design)

    Full

    Real-time co-editing: OT vs CRDT, sequence CRDT, state-vector sync, presence, offline merge, snapshots and compaction, access

  15. LLM Inference Serving and Vector Search Platform Design Template

    Full

    Gateway, router, continuous batching, paged KV cache, GPU memory and throughput math, TTFT/TPOT SLOs, autoscaling, quantization, HNSW/IVF, cost per token

    PagedAttention (Kwon et al., SOSP 2023)